The present invention relates to a chip type discharge element which discharges when a predetermined voltage is applied thereto. Such elements are used to protect electronic circuits from the application for excessive voltages.
Present electronic circuits are formed predominantly of semiconductor elements, such as transistors or integrated circuits. To protect these semiconductor elements from abnormal voltages, it is necessary to use discharge elements which discharge at low voltages.
For this purpose, discharge elements of various construction have been proposed. Examples of such known elements are shown in FIGS. 1 through 3.
The discharge element shown in FIG. 1 comprises electrode parts 14 and 15 formed at one end of lead wires 12 and 13, respectively, and encased in a glass tube 11. The electrode parts 14 and 15 are separated from each other by a small gap so that discharge takes place between the electrode parts 14 and 15. The glass tube 11 forms a sealed chamber containing an inert gas or a vacuum.
A discharge element of the foregoing type which requires a sealed glass tube 11 is expensive to manufacture, is large in size, and makes it difficult to determine the dimension of the gap.
The discharge element shown in FIG. 2 includes electrode films 23 and 24 provided on respective opposed surfaces of a disc shaped ceramic substrate 22 having a bore 21 formed at the central portion thereof. The electrode films 23 and 24 are soldered to lead wires 25 and 26, respectively, and the bore 21 is closed by two ceramic plates 27 and 28. The element as a whole is molded by an insulating resin 29, so that electrical discharge takes place between the electrode films 23 and 24 at the portions thereof surrounding the bore 21.
Such a discharge element, however, is inadequate in that many parts are required which increase the material cost, increase the size and decrease the lifetime of such discharge elements.
Further, the discharge element shown in FIG. 3 has lead wires 31 and 32 opposite to each other at ends 31a and 32a thereof within a space 34 formed in an insulating resin block 33, whereby discharge takes place between the ends 31a and 32a of lead wires 31 and 32.
A vacuum cannot be formed in the space 34 within the insulating resin block 33 with the result that the gap between the ends 31a and 32a of the lead wires 31 and 32 should be made smaller. However, the dimension of the gap is structurally difficult to obtain, especially when the size of the gap is small, thus making it very difficult to get a discharge element to discharge at low voltages.